Sonic space alarm



SEARCH RG( aaoarhaso July 31, 1962 K. H. SCHMIDT 3,047,850

somo SPACE ALARM 2 Sheets-Sheet 1 Filed Aug. l2, 1959 INVENTOR A l o mVN H ...mi NJ TGN SW A A N .Il/ pw. llvlnl i12.. IRK .S 3: d G @mm .85:#ww Swv m mm, ww A d q W( M Y N 0 W mu o o Am f .vv LV A f N5 Q J m dllMU HH A July 31, 1962 K. H. SCHMIDT soNIo SPACE ALARM Filed Aug. l2,1959 2 Sheets-Sheet 2 .W .wvl W m VN) +|.I w .1 m f N.|\ w .A I I d? mmm l Il H H s .EJ w xm 0 0 N 0 0 zo oo zo zo .to zo J. tu Q .G G: C S MQboo@ .a m 1w f d @f Q E 8f WM, .CN AVA 1/ n ON u N w w @v @www w Qn Cwmul w KQQS My invention relates broadly to protective alarm systems andmore particularly to a simplified construction of a sonic space alarmwhich utilizes the same circuits for setting up a standing wave patternand for detecting variations in the standing wave pattern.

One of the objects of my invention is to provide a sonic space alarm inwhich only one speaker or transducer unit is utilized to assist inestablishing a standing wave pattern and to accomplish the function ofdetection of standing wave variation which causes an alarm condition.

Another object of my invention is to provide a sonic space alarm systemin which the sending and receiving sources are combined into a singlecircuit.

Another object of my invention is to provide a compact transistorizedsonic space alarm which is portably selfcontained, operating on batterypower completely independent of line power.

Still another object of my invention is to provide a simplified circuitconstruction for a sonic space alarm which operates at a highsensitivity-stability ratio.

Other and further objects of my invention reside in the circuitry of mysonic space alarm as set forth more fully in the specificationhereinafter following by reference to the accompanying drawings, inwhich:

FIG. 1 is an electrical schematic circuit diagram of the oscillatorcircuit used in the sonic space alarm of my invention and particularlyshowing in schematic form the manner in which the speaker diaphragm setsup a standing wave pattern and also detects alterations in the standingwave pattern; and

FIG. 2 is an electrical schematic circuit diagram of the sonic spacealarm of my invention.

My invention is directed to a construction of a new and simplified sonicspace alarm which operates at a high sensitivity-stability ratio andutilizes a single transducer or speaker for setting up a standing wavepattern and for fulfilling the function of detection of standing wavevariation. The sonic space alarm system of my invention-sets up astanding wave pattern which is generated bywanr oscillator closelycoupled to a speaker or transducer, the combination of which is tuned toa given frequency." The standing wave pattern visu'sually restricted toa confined area but does not necessarily have to be restricted to aconfined area at sonic or ultrasonic frequencies. The speaker ortransducer is of the m gives very close coupling to air. Therefore, anychange in the standing tent wave pattern, which is closely coupled withthe *speakerN orf transducerrvaries the amplitude of the oscillatoii Thestanding wave pattern can be changed or upset by various means, such asby an intruder entering the area covered by the standing wave pattern.Any variation in the amplitude of the oscillator caused by the upsettingof the wave pattern is further amplified and fed into Va relay circuitwhich switches the system into an alarm condition.

The system will self-adjust to the existing physical characteristics ofthe area to be protected. However, after this initial self-adjustment,any variation, such as a person entering or moving about in the area,will alter the existing standing wave pattern, thus causing an alarmcondition of the system. Any movement of a foreign object can cause analteration either by absorption or ice reflection of the standing wavepattern. This can be just the movement of a door opening or any actionof an individual or object in the area.

The maximum transducer eficiency is maintained by operating thetransducer at its natural resonance and utilizing the transducer as anintimate part of the negative resistance network. The intrusioninformation is picked off from this network at a point favoring theleast loading. The derived signal is amplified through a simple low passamplifier and applied to a high reliability relay/alarm. Due to the useof semi-conductors and the inherent high efficiency of the system, it isportable in the true sense of the word. The small power consumed by thesystem permits long term operation as a self contained unit if sodesired.

Sonic space alarms are not new to the art, but other systems use twosources, one sending and one receiving, and this is not necessary in thesystem of my invention; nor is my system dependent upon Doppler effect.Those operating in the continuous wave category are convenientlyanalyzed in terms of the standing wave patterns set up by theirrespective systems.

If a pattern of standing waves is assumed for a given space systemconfiguration, certain major factors can be cited as determining factorsof system sensitivity.

These factors are as follows:

(A) The coupling coefficient between the transducer and the medium.

(B) The efficiency of the transducer.

(C) The load imposed on the transducer by the driving element.

(D) The load imposed on the transducer by the detecting circuit.

Factors (A) and (B) are determined to a large degree by the state of thetransducer art and the medium into which the transducer must work. (Inthis case air). With reference to factor (B) it can be shown thatoperation of a transducer at resonance produces the highest possibleeiciency, all other conditions being equal.

One purpose of this invention is to utilize the existing eiciency of thetransducer with circuitry, such that this efiiciency is not lost due tothe loading factors ((C) and (D) above), thus maintaining the highestpossible sensitivity versus stability.

Previous systems have attempted to make up for these losses bynon-linear amplification and filtering of the derived signal. Thisultimately leads to complex amplifiers, critical adjustments, andgenerally a loss in the sensitivitystability ratio.

Bearing in mind the requirements imposed by the loading factors statedin (C) and (D) above, we may now analyze the subject invention in theseterms.

Referring to the drawings in greater detail, in FIG. l, I have shown amodified Hartley type oscillator of my invention which I utilize in mysonic alarm, employing a semi-conductor 1 as its negative resistanceelement. In conventional design, resistors 2 and 3 set the operatingpoint. In FIG. 2 resistor 2 designates the base bias resistor which setsthe transistor operating point. Capacitor 4 completes the feedbackcircuit to the base 5 of the semiconductor. Resistor 6 would not be usedin this type circuit except in the interest of decoupling in which case,capacitor 7 would be used, to place the emitter 8 at R.F. ground.

In this invention the emitter 8 is intentionally elevated above groundand capacitor 7 is not used. The resistor 6 serves a unique set offunctions. First, it creates a high base impedance on the semi-conductor1, reducing the oscillator loading on the transducer 9. Second, resistor6 sets the oscillator circuit just above the threshold of oscillation,where it is most sensitive to the changes in its tank circuit impedance.Not so apparent is the fact that the drop across resistor 6 is inversefeed-back, hence stabilizes this operating point. The (D) loading factorpreviously mentioned, that is, the load reflected on the transducer bythe signal pick-off point is again solved by resistor 6. Since anyimpedance change in the transducer 9 will cause a direct current changein resistor 6. The change information can be removed through a simplelow pass filter consisting of filter coil 10 and filter capacitor 11,without upsetting the rest of the circuit configuration in any way.

The oscillator tuned tank circuit consists of tank capacitor 12connected across the inductance coils 13 and 13' of speaker ortransducer 9, the tank circuit being connected to the collector 14 ofthe PNP type semi-conductor 1. The oscillator circuit in combinationwith the transducer 9 sets-up or establishes a standing wave field,indicated at 20, through transducer diaphragm or acoustical forceproducing means 18. Since the transducer coils 13 and 13 in theoscillator tank circuit are tuned to their natural resonance thetransducer is thus operated at its maximum etiiciency. An intruding body19 entering the standing wave field 2t) will thereby upset the wavepattern, causing an altered standing wave pattern, indicated at 21,which, when detected, by transducer diaphragm 18, causes an impedancechange in the transducer which will change the resonant operating pointof the oscillator tank circuit. When this occurs, as previouslymentioned, a direct current change occurs across the non-inductivevariable resistor 6 connected between emitter 8 and ground, so that thetransducer is not loaded by the change information removed at signalpick-off point 22. Since emitter 8 is the point in the oscillatorcircuit which favors the least circuit loading, the current changeinformation is conveyed from this point, signal pick-off point 22, to arelay amplilier circuit through lter coil 10 and filter capacitor 11having one end thereof connected to ground.

The current change information is coupled from the output of the lowpass tilter to the base 15 of transistor amplier 16 through couplingcapacitor 17. Base bias resistors 23 and 24 connected between the base15 and ground set the operating point of transistor 16 which is of thePNP type. Bias resistor 23 is adjustable so that the operating bias oftransistor 16 may be changed, thus providing an alarm sensitivityadjustment in the relay amplier circuit. Load resistor 25 is connectedbetween the emitter 26 and ground and the transistor output informationon collector Z7 is coupled to the base 28 of NPN type transistor 29through resistor 30. Transistor 29 is normally conducting close tocut-off so that the change information appearing on the base 2.8 of therelay coupling transistor 29 operates to cut-off the energizing currentconveyed to one end of coil 32, of the normally energized alarm relay 33from the collector 31. The other end of coil 32 is connected to groundthrough ammeter 34 provided in the circuit for checking proper operatingconditions.

The change information signal from the output of transistor 29deenergizes the coil 32 of alarm relay 33 causing the movable contactor35 to move from normally closed stationary contact 37 to normally openstationary contact 36. When this occurs the external alarm circuit iscompleted, thus sounding an alarm.

Reference character 38 generally designates a three position functionswitch comprised of wafers A, B, C and D having movable switchcontactors a, b, c and d, respectively, ganged together to move inunison. In the first switch position, designated OFF, wafers A, B, C andD have no connections. Thus the battery 39, which has its positiveterminal grounded and its negative terminal connected to movable switchcontactor a, is disconnected from the circuit and the alarm system isshut off. The switch is turned to this position during the daytime hoursor while the protected area is being utilized.

In the second switch position, designated TEST, the battery 39 isconnected to the oscillator and relay amplilier circuits, and movablecontactor b through switch wafer A and its associated movable contactora. Thus in the TEST position alarm relay 33 is normally in the energizedstate. The TEST position on wafer B and the TEST and ON positions onwafer C are all commonly connected with one end of the coil 40 of delayset relay 41, the other end of the coil being grounded. Thus in thesecond switch position delay set relay coil 4t) is energized throughwafer B and contactor b, and at the same time, time delay capacitor 42connected intermediate movable contactor c and ground is charged throughwafer C. In the energized state delay set relay movable contactor 46 isin electrical contact with stationary contact 48 which has no circuitconnection. Wafer D of function switch 38 has no connection in the TESTposition, hence, there is no possibility of sounding an external alarmin this switch position.

In the TEST position, the system can be calibrated and tested withoutsounding an alarm. The alignment test jack 43 is used to align theoscillator-detector circuit. Since the relays 33 and 41 make no soundwhen they operate I provide test jacks 44 and 45, respectively,connected to normally closed stationary contact 37 and the seriescircuit commonly connecting movable contactors 35 and 46 for determiningthe relay operation state. To set the alarm sensitivtiy, an ohmeter isconnected between the test jacks 44 and 45 and observed in conjunctionwith the milliammeter 34 while the base bias resistor 23 is adjusted toproduce the desired alarm sensitivity. The emitter 47 of transistor 29is connected to the negative voltage bus and the bias resistor 23 isadjusted so that transistor 29 is in the normally conducting state sothat coil 32 of relay 33 is normally energized. In the energized statethe movable contactor 35 of relay 33 is in electrical contact withnormally closed contact 37. Bias resistor 23 positions transistor 29very close to cut-off so that any change information from the detectorcircuit will cut-otf the transistor 2,9, thus deenergizing coil 32 andcausing movable contactor 35 to move into electrical contact withnormally open alarm control stationary contact 36.

The third position on the function switch 38 is the normal operatingposition designated ON. In this position my sonic alarm system is fullyoperational. The circuit functions are as follows:

(1) Wafer A maintains connection between the battery 39 and theoscillator and relay amplifier circuits.

(2) Wafer B disconnects the battery from delay set relay coil 40.

(3) Wafer C maintains the connection between time delay capacitor 42 andcoil 4t) of the delay set relay 41.

(4) Wafer D connects the stationary contact 49 of delay set relay 41 tothe alarm connection circuit 50, thus connecting the external alarm 51through the series contacts of relays 33 and 41.

Since time delay capacitor 42 is charged in the TEST position it isfully charged at the instant the function switch is switched to the O=Nposition, thus relay coil 40 remains energized until capacitor 42discharges through the coil `40 of the delay set relay to ground. Thisdischarge time is approximately one minute, being dependent upon theresistance of the coil 40, the value of capacitor 42, and the dropoutvoltage of relay 41. The purpose of this delay in setting the relay tocomplete one part of the alarm circuit is to allow setting the alarm andleaving the area without triggering the external alarm circuit 51. Whencapacitor 42 discharges to the dropout voltage of relay 41 the movablecontactor 46 thereof moves into electrical contact with stationarycontact 49 which is connected to external alarm circuit 51 throughcircuits 50 and 52. Thus it can be seen from FIG. 2 that a connectionbetween contact 36 and movable contactor 35 is all that is required tocomplete the series alarm closure circuits which extend from the alarmcircuit 51, over circuit 53, through the contacts of relays 33 and 41which are connected in series, and then back to the alarm circuit 51through circuits 52 and 50.

The connection between contact 36 and movable contactor 35 is broughtabout by an intruding body upsetting or altering the standing wave fieldas previously set forth. 5

The charge information from the detector circuit results in cutting othe normally conducting transistor 29 which causes normally energizedrelay coil 32 to be deenergized, thus causing movable contactor 35 todrop into electrical contact with stationary contact 36 to complete ashort 10 circuit across the input terminals to the alarm circuit 51,thus actuating an alarm.

The external alarm circuit 51 is complete in itself. It contains its ownbatteries and alarm duration timing circuit. terminals of the externalalarm, such as between circuits 50 `and 53, will energize the alarm andits associated timing circuit. The audio alarm continues until theinternal timing circuit shuts it off. The timing circuit is preferablyset for an approximate two minute interval. shut olf, the external alarmcircuit 51 remains silent until the input is again momentarily Shorted,thus reenergizing the audio alarm and its timing circuit.

The sonic alarm of my invention can operate in both the audiblefrequency range and the inaudible frequency range, the frequency rangeof operation depending upon the individual alarm application. Mypreference is to operate my sonic alarm inthe inaudible frequ e r 1cyraggaM l,

thus making the intrusion alarm application more realistic.

I can summarize the salient points of my invention by stating itsadvantages over other devices intended for space alarm applications, asfollows:

`(l) The simplicity of the circuit without sacrifice of reliability orsensitivity.

(2) The high inherent stability of operation point due 35 to thecombination of a transducer at resonance functioning as the main tankcircuit of a unique semi-conductor oscillator.

(3) The availability of a single control summation point Whose positionin the circuit provides a non-loading sig- 40 nal pick-olf.

I have constructed and tested the sonic space alarm of my invention landhave found it very useful, practical, and stable while maintaining highsensitivity. It has proved to be an extremely reliable and accurateprotective lalarm system.

While I have described my invention in certain preferred embodiments Irealize that modifications may be made and I desire that it beunderstood that no limitations upon my invention are intended other thanmay be imposed by the scope of the appended claims.

What I claim yas new and desire to secure by Letters Patent of theUnited States is -as follows:

l. A sonic space alarm wave pattern establishing and detecting systemcomprising a transducer carrying windings thereon, said transducer beingof a type that gives very close coupling to air, a transistor oscillatorhaving a tank circuit, said transistor oscillator having a collector,base and emitter, said tank circuit comprising a capacitor connectedacross the transducer windings, said tank circuit connected to thecollector, a Ifeed-back capacitor connecting said tank circuit to saidbase, said base connected to a power source through -a bias resistor,said emitter providing a signal pick-off point, means connecting saidsignal pick-off point to ground, a low 3. A sonic space alarm as setforth in claim 1 in 75 In operation, a momentary short across the input15 After being 20 which said means connecting said signal pick-olf pointto ground is a variable resistor.

4. A sonic space alanm as set forth in claim l in which said meansconnecting said signal pick-off point to ground is a non-inductiveresistor.

5. A sonic space alarm as set forth in claim l in which said meansconnecting said signal pick-off point to ground is a non-inductivevariable resistor.

6. A sonic space alarm system comprising a transducer of a type thatgives very close coupling to air, said transducer including coils, and atransducer acoustical force producing means, said transducer acousticalforce producing means coupled through coupling means to said transducercoils, a standing Wave generating transistor oscillator having acollector, a base, an emitter and a tank circuit and including atransistor having a collector, an emitter and a base, said transducercoils in conjunction with a capacitance constituting said tank circuit,said tank circuit being connected to the oscillator collector member,said oscillator further having a signal pick-off point connected to theoscillator emitter, and alarm circuit means connected to said signalpick-off point, said alarm circuit means being responsive to theamplitude at said Signal pick-off point.

7. A sonic space alarm standing wave establishing and detecting-"systemcomprising a transducer of the type that gives very close coupling toair, said transducer including coils and a transducer acoustical forceproducing means, a standing wave generating oscillator circuit, saidoscillator circuit including a tank circuit, said coils being disposedin the tank circuit of said oscillator circuit, an oscillator signalpick-off point, said oscillator circuit being effective to cause saidtransducer acoustical force producing means to simultaneously establisha standing Wave pattern and detect variations in the standing wavepattern, variations in said standing wave pattern causing changes in theimpedance of said transducer coils whereby the amplitude of the signalsat said signal pick-off point is varied, and signal amplitude responsivealarm means interconnected to said signal pick-oftr point.

8. A sonic space alarm system having a standing wave establishingoscillator circuit, a standing wave variation detection circuit, atransducer -having an acoustical force producing means therein, saidtransducer being of a type that gives very close coupling to air, saidoscillator circuit and said acoustical force producing means beingeffective to produce a steady state wave pattern, said steady state wavepattern being altered by the intrusion of a body into said pattern, adetection circuit, said acoustical force producing means being coupledwith said oscillator circuit and said detection circuit and beingeffective to simultaneously establish said standing wave pattern anddetect any variations in said standing wave pattern, and alarm circuitmeans responsive solely to changes in the amplitude of oscillationsgenerated in said oscillator for providing an alarm upon the occurrenceof a variation in said standing wave pattern.

9. A sonic space alarm system having a standing wave establishingoscillator circuit, a standing wave variation detection circuit, atransducer having an acoustical force producing means therein, saidtransducer being of a type that gives very close coupling to air, saidoscillator circuit being effective to oscillate said -acoustical forceproducing means -at the natural resonant frequency of said acousticalforce producing means, said oscillator circuit and said acoustical forceproducing means being effective to produce a steady state wave pattern,said steady state wave pattern being altered by the intrusion of a bodyinto said pattern, said acoustical force producing means being coupledwith said oscillator circuit and said detection circuit and beingeffective to simultaneously establish said standing wave pattern anddetect any variations in said standing Wave pattern, Iand alarm circuitmeans responsive solely to changes in the amplitude of oscillationsgenerated in said oscillator for providing an alarm upon the occurrenceof a variation in said standing wave pattern.

10. A sonic space alarm comprising an oscillator circuit, a detectioncircuit, a speaker including a diaphragm land means including a coil forvibrating said diaphragm, said coil being connected in the tank circuitof said oscillator, said speaker being of a type that gives very closecoupling to air, said oscillator circuit being effective to cause saidspeaker diaphragm to be vibrated at its resonant frequency whereby lasteady state wave apttern is produced, said steady state Wave patternbeing altered by the intrusion of a body into said pattern, saiddetection circuit being coupled with said oscillator circuit and saidspeaker winding, said speaker being effective to simultaneouslyestablish a steady state Wave 15 2,901,716

References Cited in the iile of this patent UNITED STATES PATENTS2,031,951 Hartley Feb. 25, 1936 2,826,753 Chapin Mar. 1l, 1958 2,832,950Snyder Apr. 29, 1958 2,899,648 Gregory Aug. 11, 1959 Brown et al. Aug.25, 1959

